From c26f01eefdf8c28881db7b6f8b8fd6120a3ad68e Mon Sep 17 00:00:00 2001
From: Jerome Eteve <jeteve@users.noreply.github.com>
Date: Tue, 6 Jun 2023 15:26:50 +0100
Subject: [PATCH] client checks kernel module in /sys/module for WSL2 bridge
 networking (#17306)

---
 .changelog/17306.txt                    |  3 +++
 client/fingerprint/bridge_linux.go      | 16 ++++++++++++++++
 client/fingerprint/bridge_linux_test.go |  4 ++--
 3 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 .changelog/17306.txt

diff --git a/.changelog/17306.txt b/.changelog/17306.txt
new file mode 100644
index 000000000..683c410d3
--- /dev/null
+++ b/.changelog/17306.txt
@@ -0,0 +1,3 @@
+```release-note:improvement
+client: check kernel module in `/sys/module` to help with WSL2 bridge networking
+```
diff --git a/client/fingerprint/bridge_linux.go b/client/fingerprint/bridge_linux.go
index e351c384b..10f0e78b6 100644
--- a/client/fingerprint/bridge_linux.go
+++ b/client/fingerprint/bridge_linux.go
@@ -56,6 +56,14 @@ func (f *BridgeFingerprint) detect(module string) error {
 	// accumulate errors from every place we might find the module
 	var errs error
 
+	// Check if the module is in /sys/modules
+	sysfsModulePath := fmt.Sprintf("/sys/module/%s", module)
+	if err := f.findDir(sysfsModulePath); err != nil {
+		errs = multierror.Append(errs, err)
+	} else {
+		return nil
+	}
+
 	// check if the module has been dynamically loaded
 	dynamicPath := "/proc/modules"
 	if err := f.searchFile(module, dynamicPath, f.regexp(dynamicModuleRe, module)); err != nil {
@@ -89,6 +97,14 @@ func (f *BridgeFingerprint) detect(module string) error {
 	return errs
 }
 
+func (f *BridgeFingerprint) findDir(dirname string) error {
+	if _, err := os.Stat(dirname); err != nil {
+		return fmt.Errorf("failed to find %s: %v", dirname, err)
+	} else {
+		return nil
+	}
+}
+
 func (f *BridgeFingerprint) searchFile(module, filename string, re *regexp.Regexp) error {
 	file, err := os.Open(filename)
 	if err != nil {
diff --git a/client/fingerprint/bridge_linux_test.go b/client/fingerprint/bridge_linux_test.go
index 37d0acd5e..16581ba3c 100644
--- a/client/fingerprint/bridge_linux_test.go
+++ b/client/fingerprint/bridge_linux_test.go
@@ -19,11 +19,11 @@ func TestBridgeFingerprint_detect(t *testing.T) {
 	ci.Parallel(t)
 
 	f := &BridgeFingerprint{logger: testlog.HCLogger(t)}
-	require.NoError(t, f.detect("ip_tables"))
+	require.NoError(t, f.detect("kernel")) // kernel should be there.
 
 	err := f.detect("nonexistentmodule")
 	require.Error(t, err)
-	require.Contains(t, err.Error(), "3 errors occurred")
+	require.Contains(t, err.Error(), "4 errors occurred")
 }
 
 func writeFile(t *testing.T, prefix, content string) string {